1. (Field of the Invention)
The present invention relates to a vibration control apparatus for vehicles, and more particularly to a vehicle vibration control apparatus which is well suited to improve the riding quality of a railway vehicle
2. (Description of the Prior Art)
A vehicle vibration control apparatus in a prior art is so constructed that the vibrations of a vehicle body are detected as an acceleration or a displacement relative to a truck, to compensate for the detected results and produce a control signal for suppressing the vibrations of the vehicle body, whereupon a fluid operating mechanism capable of controlling the relative displacement between the vehicle body and the truck is actuated with the control signal so as to suppress the vehicle body vibrations. That is, the amount of protrusion or retraction of the fluid operating mechanism is controlled, whereby the relative displacemeht between the vehicle body and the truck is adjusted, and vibrations to be transmitted to the vehicle body are suppressed. Besides, in order to produce the optimum value as the control signal, a circuit for compensating the detected result of the vibrations is constructed of an integral element, a first order lead element and a first order lag element.
As the vibration control apparatus for vehicles, an example disclosed in the U.S. Pat. No. 4,402,527 has heretofore been known.
With such a vehicle vibration conlroI apparatus, the peak of the first resonance point of the vehicle vibrations can be sharply reduced. Meanwhile, in the vehicle furnished with the vehicle vibration control apparatus, a spring system for supporting the vehicle body includes a dashpot being a damping mechanism in order to ensure the riding quality in the ordinary running state even when the vibration control apparatus is not operated. Accordingly, while the vibration control apparatus is operated, mechanical and uncontrollable damping is exerted by the dashpot. In regard to the characteristic of the dashpot, there is no problem in a frequency range lower than the first resonance point as described above. In a frequency range higher than the first resonance point, however, a phenomenon which cancels out the control effect of the vibration control apparatus arises. Thus, in the higher frequency range, vibrations might increase more than in the case where the vibration control apparatus is not operating.
The above phenomenon will be explained in more detail. In the prior-art vehicle vibration control apparatus, letting y.sub.o denote track irregularities in lateral directions and y denote the yawing of the vehicle body, the response magnification y/y.sub.o of the vehicle body varies as shown in FIG. 9 with respect to the frequency of vibrations. In the figure, letter A indicates the state of a setup which has the damping mechanism in the spring system for supporting the vehicle body, without employing the vibration control apparatus, letter B indicates the state of a setup which has both the damping mechanism and the vibration control apparatus, and letter C indicates the state of a setup which has only the vibration control apparatus without employing the damping mechanism. As seen from the figure, in the state B compared with the state A, the peak of the first resonance point in the vicinity of 1 Hz can be sharply lowered, but the response magnification becomes larger values contrariwise in a frequency range of 2 Hz-7.5 Hz. In the prior-art vehicle vibration control apparatus, therefore, the dashpots are not taken into sufficient consideration.